Refrigeration equipment for providing cold storage of articles, such as residential refrigerators for storing food items, include several different temperature zones, or compartments. Common among these are a freezer compartment for maintaining sub-freezing temperatures, and a fresh food compartment for maintaining a cool temperature for fruit and vegetable produce. The known method of regulating the different compartment temperatures is to use a compressor, evaporator, and fan to provide sub-freezing air to the freezer compartment, and to bleed some of this air to cool the fresh food compartment, as necessary, to maintain the fresh food temperature between freezing and room ambient.
There are several known prior art control methods and systems for achieving this. The least cost method is to use a manually operated damper in the bleed line and a thermostat in the fresh food compartment. The refrigerator user then adjusts the damper position and the thermostat set point temperature to selected values. The thermostat then actuates the refrigeration system (i.e. compressor and evaporator fan) to control the cool air flow to the freezer in response to the actual fresh food compartment temperature being above and below the thermostat set point. The freezer temperature then is dependent on the fresh food compartment set point temperature and the damper position. This has several drawbacks, including the instability of the freezer temperature, as well as longer operating cycle times of the compressor and evaporator fan. This results in higher operating costs due to the lower electrical efficiency of the refrigeration system.
A less common, but more expensive type control system used in “high performance” refrigerators (approximately 15% of the refrigerators produced in the United States) is to use a freezer compartment thermostat to control actuation of the refrigeration system and to modulate the cool air flow to the fresh food compartment with a damper which is automatically positioned by a refrigerant charged bellows. The bellows expands and contracts in response to the fresh food compartment temperature, and positions the damper in a manner to maintain the fresh food compartment temperature within a user selected temperature range. This provides direct control of the freezer temperature, and since the bellows temperature characteristics are predictable, this system provides more accurate temperature control of both compartments.
Despite the improved efficiency of the more expensive system, the controlled temperature of both compartments still varies over a substantial range of temperatures. This is due to the passive nature of both of these control functions, which is characterized by greater operating tolerances as well as limited response time. Alternatively, the growing use of microcontroller and microprocessor based controls in residential appliances now makes them cost effective for use in residential refrigerators. They provide increased control accuracy, faster response, and lower refrigeration cycle times, all of which result in higher efficiency and lower operating costs to the consumer.
Within these electronic control type systems, however, there remains the need for mechanical damper assemblies. To further improve the operating efficiency of the electronic controls, these mechanical damper assemblies must preferably be capable of operating in a gated manner; i.e. in an open/closed sequence at a given duty cycle, as determined by the electronic control. The ideal damper assembly therefore must itself be capable of fast response as well as efficient air flow characteristics.
A rotary damper assembly resolves many of these concerns. In such an assembly, an inner cylinder is provided within an outer cylinder (or housing) and is rotatable within this outer cylinder. The inner cylinder contains an inlet aperture and an outlet aperture, and the outer cylinder also contains an inlet aperture and an outlet aperture. The inner cylinder, which is nested within the outer cylinder, is rotated by a motor to adjust the registration of the outlet apertures of the inner cylinder and the outer cylinder. When the outlet apertures are fully registered, the damper is considered fully open and the maximum flow rate through the damper is provided. When the inner cylinder is rotated to a position in which the outlet apertures are fully deregistered, the damper is in a closed position in which a minimum flow rate of fluid is provided.
While such a rotary damper overcomes many of the concerns in the prior art, there may still be an undesirable amount of air leakage when the damper is in the closed position. Furthermore, it is desirable to increase the reliability of the rotary damper.